The objective of the proposed research is to investigate labile self- esteem (SE) and ruminative responses to dysphoric moods in previously depressed (n=20) and never-depressed control participants (n=20). This "remission design" can help determine whether or not labile SE and rumination are stable trait factors that potentially could play a role in vulnerability to Major Depressive Disorder (MDD). Previously depressed individuals will be recruited from an ongoing treatment study and never-depressed control participants will be matched on age, gender, and ethnicity. Self-esteem, rumination, mood, and daily stressors will e assessed for 45 consecutive days using hand-held computer diaries. Daily assessments will provide a powerful approach to investigating both between-participant factors (based on aggregate measures), as well as dynamic within-participant processes (based on aggregate measures, as well as dynamic within-participant processes (based on the disaggregated time-series data. The former will focus on characteristics such as average level of SE and rumination, whereas the latter will focus on SE's reactivity to stress and mood, as well as the impact of rumination (on a given day) on the duration of dysphoric moods. The proposed research will test the hypotheses that relative to never depressed controls, individuals who have recently remitted from an episode of Major Depression will exhibit: (1) labile SE (operationalized as instability and as reactivity to daily events and moods); and (2) a ruminative responses style to dysphoric moods. In addition, the proposed research will examine the degree to which co-morbid Anxiety Disorders, Axis II pathology, dysfunctional attitudes, low SE, negative attributional system, and neuroticism contribute to labile SE and ruminative response style. Finally, this research will test the hypothesis that rumination in response to a negative mood on a given day is associated with the duration of that mood, and will explore possible moderators of this relationship (such as depression history). This research will help identify characteristics and processes that potentially contribute to vulnerability to MDD. Such knowledge could ultimately contribute to the development of more effective treatment interventions that more directly target core processes in this disorder.